Airplane heater having pressure differential fuel control



Sept. 23, 1947. 'L' A, wlLLlAMs, JR 2,427,758

AIRPLANE HEATER HAVING PRESSURE DIFFERENTIAL FUEL CONTROL Filed Feb. 19, 1943' 2 Sheets-Sheet l Sept 23, 1947- i 1 A. WILLIAMS, JR y2,427,758

AIRPLANE HEATER HAVING PRESSURE DIFFERENTIAL FUEL CONTROL Filed Feb. 19, 1943 2 Sheets-Sheet 2 changer 20.

Patented Sept. 23, 1947 AIRPLANE HEATER HAVING PRESSURE DIFFERENTIAL FUEL CONTROL Lynn A. Williams, Jr., Northfield, Ill., assignor to Stewart-Warner Corporation, Chicago, Ill., a corporation of Virginia Application February 19, 1943, Serial No. 476,429 7 Claims. (Cl. 158-28) l My invention relates to heater carbureting systems. and more particularly to the carbureting systems of heaters intended for use in airplanes, or other purposes, in which relatively great changes in altitude are present.

An .object of my invention is to provide a heater carbureting system wherein the fuel is supplied to the heater under pressure, so that no additional pressure drop across the heater is required to supply the fuel thereto, as is necessary in the conventional Venturi type of carburetor, and wherein further mean's is provided to compensate the fuel supply means for changes in altitude to" prevent the fuel mixture supplied from becoming excessively rich at high altitudes.

A further object of my invention is to accomplish the foregoing object by means of a simple, light, inexpensive, and durable structure, having a minimum of moving parts, and capable of long life.

Other objects and advantages will become apparent as the description proceeds.

' In the drawings:

Fig. 1 is a view showing one embodiment of my invention, and wherein the heater is shown in longitudinal section for clearer illustration;

Fig. 2 is a longitudinal sectional view of the fuel supply means shown in the upper part of Fig. l; and

Fig. 3 is a view taken on the line 3-3 of Fig. 2.

In Fig. 1, I have illustrated my invention as being used in connection with an internal combustion type of heater, having a combustion chamber I il supplied with combustible mixture from an induction-pipe l2 communicating with the combustion chamber through slots I4. An electrical igniter I6 serves initially to ignite the combustible mixture supplied to the combustion chamber i0, and is ordinarily provided with a thermostatic switch which disconnects it from its source ofV electrical current when the heater attains normal operating temperature. A reigniter I8 is provided to insure maintenance of combustion after the igniter i6 has been disconnected from its source of electrical energy.

The hot products of combustion formed in the combustion chamber I flow from the right-hand end of this chamber into a tubular heat exchanger 20 of the hollow fin type. The ends of the hollow ns are sealed, as indicated at 22 and 24. A muffler 26 directs the hot products of combustion into the left-hand ends of the hollow ns, and as the hot gases traverse these fins, the heat from the gases is transmitted to the heat ex- The cooled gases flow from the 2 right-hand ends of the hollow fins into an outlet chamber 28, which communicates wi"i atmosphere through a discharge fitting 30 and any suitable exhaust pipe which may be attached to the threaded end 32 of this fitting.

I'he muiller 26 Ahas a sheet metal shell 34 provided with openings 36 forming acoustic couplings between the gas passages and the interior of the muliler, which is filled with sound absorbing material 38, such as stainless steel wool or glass wool. The muiiler may be provided with a nose 40 forming an empty acoustic chamber 42 connected by openings 44 to the interior of the main part of the mufller.

A fuel jet 46 is located in the induction pipe I2 and is supplied with fuel by a pressure fuel supply means indicated generally by the reference character 48, and connected to the jet 46 by a pipe 50. The fuel supply means 48 operates on the di'erence in pressure between the combustion chamber Ill and the inlet of a ram 52 which is connected to the pressure device 48 by a pipe 54. Pipe 56 connects the fuel supply means 48 with the combustion chamber l0. A pipe 58 connects the fuel supply means with a fuel pump, elevated tank, or other source of fuel under pressure.

Referring toFig. 2, it will be seen that communication between the fuel pipe 58 and a cham- Iber 60 is controlled by a valve 62 which is moved to closed position by a lever 64 pivoted on an adjustable support "i This I support may be shifted by an adjusting screw 68 against which the support is urged by a spring 1li. The other end of the lever 64 is pivotally connected to an operating rod 12 attached to a disc 14, closing one end of a bellows 16.

The other end of the bellows 16 is attached to the wall 18 of a casing 80 so that the interior of the bellows 16 constitutes a variable chamber in communication with the ram 52 through the pipe 54. That part of the casing which is external of the bellows 16 and disc 14, constitutes a second variable chamber 82 which communicates through pipe 56 with the combustion chamber I0. The disc 14 is thus subjected to the differences in pressure between the combustion chamber I0 and ram 52, and this dilerence in pressure controls the position of the valve 62 and also the pressure in the fluid chamber 60, which extends into the interior of a bellows 84 surrounding the valve operating rod l2. The difference in pressure between the ram 52 and combustion chamber i0 acts over substantially the entire area of the disc 14 and the force thus created in the fuel chamber 60 to force this fuel to the j The combustion chamber I and heat exchanger 20 are surrounded by a cylindrical casing 86 which is connected to an air inlet 88 attached to the usual ram. In the particular form of my invention shown in the drawings, the same ram and inlet provide the combustion air for the induction tube i2. Ventilating air flows between the heat exchanger 20 and casing 86, and picks up heat from the heat exchanger. The heated Ventilating air flows from the right-hand end of the casing 86 directly into a cabin or other space to be heated. or into a duct system having outlets at selected locations.

When such a heater is installed on an airplane in flight, the air supply, of course, varies as the airplane changes its altitude. At higher altitudes, the air is rarefied so that the mass ow will be reduced if the velocity of air flow through the heater remains the same; but frequently the airplane maintains higher speeds at higher altitudes, thus altering the velocity of air flow. It will simplify consideration of the present invention to consider the effect of changes of altitude with tne mass ow of air maintained at a. uniform rate. For example, when an airplane provided with a. heater of this type increases its altitude, the pressure drop between the ram 52 and the combustion chamber I0 will increase, if it be assumed that the mass flow of air is kept constant, as by increasing the speed of the airplane enough t0 compensate for the reduced density of the air at the higher altitude. But this increase in the pressure drop would actuate the bellows 16 in a manner to increase the richness of the mixture supplied to the combustion chamber, unless compensating means were provided, and a feature of my invention lies in the provision of such means.

This altitude compensating means may assume various forms, the particular means shown being that disclosed and claimed in the copending application of William A. Marshall, Jr., Serial No. 480,974, filed March 29, 1943, now Patent No. 2,381,358, issued August 7, 1945. The function of this compensating means is to control the escape of air from the interior of the bellows 16 and thereby reduce the dierential pressure on opposite sides of the disc 19.

In Fig. 2, there is clearly illustrated a tube 90 projecting into the interior of the bellows 16 and provided with a longitudinal slot 92. A valve 94 is slidable in the tube 90 and regulates the escape of air from the interior of the bellows 16 by way of slot 92 and tube 90.

The valve 94 has a stem 96 attached to the end 98 of an evacuated bellows |00 supported in a housing 202 by an adjustable screw |04. A spring |06 tends to expand the bellows |00 and move the valve 94 toward open position. The bellows |00 is collapsed by the pressure in the chamber |08 surrounding this bellows. VThis chamber communicates by way of pipes I0 and 56 with the interior of the combustion chamber I0, so that the pressure in the chamber |09 varies with the pressure in the combustion chamber.

In the operation of my heater carbureting system, the air supplied by the main ram creates a pressure at the inlet of the ram 52 which ls greater than the pressure' in the combustion chamber i0. This diierence in pressure acts on opposite sides of the disc 14, moving this disc to the left and permitting valve 62 to open. Fuel iiows under pressure into the fuel chamber 60 and is supplied to the Jet 4B under a pressure determined by the pressure diiferential on opposite sides of the disc 14. As heretofore explained, the pressure in the fuel chamber 60 is much greater than the pressure difference on opposite sides of the disc 14, but if the pressure in the fuel chamber 60 rises to too great a value, disc 14 is moved to the right and valve 62 is closed or moved toward closed position to reduce the rate of fuel supply to the chamber 80.

With increases in altitude, if the mass ow of air be kept constant the pressure differential between the ram 52 and combustioncha'nber increases, but the absolute pressure in the combustion chamber I0 decreases. This decrease in pressure is communicated to chamber |08, permitting bellows |00 to expand and move valve 94 to uncover a portion of slot 92. 'Ihe uncovered portion will vary in length with the altitude attained. Air escaping from the interior of bellows 16 through slot 92 will prevent the pressure differential across disc 14 from increasing with the increase in altitude, and will maintain a lniformly rich mixture supply for the combustion chamber. The air escaping through slot 92 passes into chamber |09 and through pipes ||0 and 56 to the combustion chamber.

While I have illustrated and described only one embodiment of my invention, it is to be understood that my invention is not limited to the details shown and described. but may assume numerous other forms, and that my invention is defined in the following claims.

I claim:

1. In combination with a heater having a combustion chamber and an induction tube leading thereto, a carbureting system comprising a fuel jet located in said induction tube, means forming a fuel chamber connected to said jet. said fuel chamber having an inlet adapted to be connected to a source of fuel under pressure. a valve controlling admission of fuel through said inlet, an expansible bellows operative on expansion to move said valve in opening direction, a casing enclosing said bellows, a pipe connecting the lnside of said bellows with said induction tube, and a pipe connecting the space between said bellows and said casing with said combustion chamber.

2. In combination with an airplane heater having a combustion chamber and an induction tube leading thereto, a carbureting system comprising a first bellows enclosed in a casing, means connecting the interior of said bellows with said induction tube, means connecting the interior of said casing with said combustion chamber whereby said bellows is responsive to differences in pressure between said induction tube and combustion chamber, means forming a fuel chamber including a second bellows engaging said first mentioned bellows, said fuel chamber being adapted for connection to a source of fuel under pressure, a pipe connecting said fuel chamber with said induction tube for discharge thereinto, and a valve controlling admission of fuel to said fuel chamber and connected to said bellows for movement in opening direction in response to expansion and in closing direction in response to contraction of said first bellows, together with a vent valve for the first bellows and means automatically shifting said vent valve in opening direction in response to decreases in atmospheric pressure and in closing direction in response to increases in atmospheric pressure.

3. In combination with a heater having a combustion chamber and an induction tube leading thereto, a carbureting system comprising a fuel Jet located in said induction tube, means forming a fuel chamber in communication with said jet, a valve controlling communication between said fuel chamber and a source of fuel under pressure, a relatively small bellows having its` interior in communication with said fuel chamber and forming a part thereof, a relatively large bellows having a common wall with said first mentioned bellows, means operatively connecting said valve to said wall whereby said valve opens in response to expansion of and closes in response to contraction of said large bellows, said bellows being arranged to expand and contract in opposition to each other, a casing supporting and enclosing both of said bellows and forming a, space surrounding said bellows, means connecting said space with said combustion chamber, a ram located in said induction tube, and means'connecting the interior of said larger bellows with said ram.

4. In combination with a heater having a combustion chamber and an induction tube leading thereto, a carbureting system comprising a fuel jet located in said induction tube, means forming a fuel chamber in communication with said jet, a valve controlling communication between said fuel chamber and a source of fuel under pressure. a relatively small bellows having its interior in communication with said fuel chamber and forming a part thereof, a relatively large bellows having a common wall with said rst mentioned bellows, means operatively connecting said valve to said Wall whereby said valve opens in response to expansion of and closes in response to contraction of said large bellows, said bellows being arranged to expand and contract in opposition to each other, a, casing supporting and enclosing both of said bellows and forming a space surrounding said bellows, means connecting said space with said combustion chamber, a ram located in said induction tube, means connecting the interior of said larger bellows with said ram, and an altitude compensator controlling the escape of air from said larger bellows to prevent the difference in pressure between the interior of said larger bellows and said space from lncreasing with increases in altitude.

5. In combination with a heater having a combustion chamber and an induction tube leading,v

thereto, a carbureting system including means Number forming a fuel chamber, a jet in said induction tube, a pipe connecting said jet and fuel chamber, means for connecting said fuel chamber to a source of fuel under pressure, a valve controlling communication between said source and said fuel chamber, a lever for regulating the position of said valve, a support to which said lever is pivoted, a spring urging said support in one dlrection, a screw for moving said support in opposition to said spring, and means responsive to the pressure differential between said induction tube and said combustion chamber for shifting said lever in valve opening. direction with increases in said pressure differential and in valve closing direction with' decreases in said pressure differential.

6. In the combination defined in claim 1, an air vent for said bellows, a second casing into which said vent discharges, an evacuated bellows in said second casing, a regulating valve for said vent connected to said evacuated bellows for movement in opening direction in response to expansion and in closing direction in response to contraction of said evacuated bellows, and a conduit connecting said second casing with the combustion chamber.

7. In the combination dened in claim 3, means for regulating the ram pressure applied to said larger bellows, comprising a, second casing, a vent connecting said casing with said bellows, a valve controlling said vent, an evacuated bellows mounted in the second casing and operatively connecting to said vent valve whereby said vent valve is moved in opening direction in response to expansion of and in closing direction in response to contraction of said evacuated bellows, and conduit means connecting said second casing with the combustion chamber for actuating the vent valve in response to changes of atmospheric pressure and also conducting to said combustion chamber the air vented from said larger bellows.

LYNN A. WILLIAMS, JR.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Name Date Donaldson Oct. 31, 1939 Merkt Oct. 3, 1939 Keith Dec. 28, 1920 FOREIGN PATENTS Country Date Great Britain July 25, 1940 Number Certicate of Correction i Patent No. 2,427,758. September 23, 1947.

' LYNN A. WILLIAMS, Jn.

It is hereby certied that errors appear in the printed specification of the above l numbered patent requiring correction as follows: Column 3, line 64, for. the numeral 202 read 102; column 6, line 33, claim 7, for connecting read connected; and that the said Letters Patent should be read with these corrections therein that the same .may conform to the record of the casein the Patent Ofce.

Signed and sealed this 17th day of February, A. D. l1948.

THOMAS F. MURPHY,

Assistant ommz'ssioner of Patente. 

